The present invention relates to the field of sigma delta modulators.
Sigma delta modulators are becoming increasingly important in the DSP processing field and are useful in A/D conversion, one bit processing etc.
For a full discussion of the operation of Sigma Delta modulators, reference is made to one of the standard texts in the field. For example, xe2x80x9cDelta-Sigma Data Convertersxe2x80x94Theory, Design and Simulationxe2x80x9d, S. Norsworthy et. al., published 1997 by IEEE Press Marketing.
In any Sigma-Delta modulator, it is important to provide as faithful a reproduction or quanization of the original signal as possible. Importantly, any low frequency noise introduced in the quantization should be of as low an amplitude level as possible.
It is an object of the present invention to provide an improved form of Sigma Delta Modulator.
In accordance with a first aspect of the present invention, there is provided a sigma delta modulator apparatus comprising: input means for inputting a current input signal; differencing means for forming the difference between a current input signal and a current output signal; filtering means for filtering the difference so as to produce a filtered difference signal; output means outputting a minimum or maximum output value so as to substantially minimize the filtered difference signal.
The filter can be of the form:
G(z)=1+zxe2x88x921xc2x7H(z)
In accordance with a further aspect of the present invention, there is provided a sigma delta modulator comprising: a differencing means for forming the difference between a current input signal and a current output signal to produce a difference output; delay means for storing and delaying the difference output, producing a delayed difference output; low pass filtering means for low pass filtering the delayed difference output producing a low pass output; summing means for summing the delayed difference output with a current input signal; to produce a current intermediate output; and quantizing means for quantizing the current intermediate output to a predetermined number of output states producing an output signal.
In accordance with a further aspect of the present invention, there is provided a method of computing a first series of B output signals samples from a second series of B input signals comprising the steps of: (a) computing the difference between a current input series and each possible output series; (b) for each of the possible output series, determining a low frequency part of a successive series of the differences; (c) amplifying the low frequency parts; (d) utilizing an output signal having a minimum low frequency part as an output signal.